Performance, response surface, energy, exergy and economic analyses of a biomass engine-thermoelectric-thermosyphon hybrid system for sustainable power generation via waste heat recovery

The depletion of fossil fuels and rising global energy demand have intensified concerns over climate change, environmental degradation, and energy security, highlighting the need for efficient waste heat recovery-based renewable energy solutions. The present study proposes a novel renewable energy-driven biomass engine-thermoelectric-thermosyphon hybrid system for sustainable power generation and it is investigated experimentally with statistical optimization. A Box-Behnken design comprising 15 experiments is employed to develop regression-based correlation models and apply response surface methodology for optimizing key parameters, influence of various input factors and their contibutions through senstivity analysis. The thermodynamic performance and feasibility of system is evaluated through integrated energy-exergy and scalability-economic analyses. The results indicate that a maximum electrical output of 0.591 W is achieved from waste heat at optimal conditions. The predictive models exhibit good agreement with experiments, achieving accuracy above 98%. Sensitivity analysis identifies vacuum pressure as the dominant parameter (50-53%), followed by source temperature (26-32%) and filling ratio (12-17%), highlighting that higher pressure and temperature with a mid-level filling ratio yields an optimal performance. The system processes 55.26 kW of total biomass input energy with 65% gasification efficiency and 35% of syngas fuel energy available as recoverable waste heat, enabling cascade utilization for thermoelectric power generation and biomass drying. The thermoelectric subsystem exhibits an energy and exergy efficiencies of 1.8% and 4.02% respectively. The economic analysis reveals that the 500 kW configuration achieves the lowest electricity generation cost (4.83 INR/kWh) with a payback period of nearly 5 years, demonstrating strong competitiveness against diesel and conventional thermal power generation. The findings confirm the techno-economic feasibility, scalability, and sustainable decentralized energy potential of the proposed hybrid system.